The plain old telephone service, or POTS, is the service that delivers analog voice signals to a customer's home or office. These analog voice signals are generally transmitted at a frequency of less than 4 kHz via twisted pairs of copper wires. These same twisted pairs of wires often carry digital signals at significantly higher frequencies. For example, a twisted-pair wire may carry a very high digital subscriber line (VDSL) signal operating in the range of 25 kHz to 8.5 MHz, and above.
When such an incoming signal is received at a customer premise, it must be split into separate low- and high-frequency signals. The low-frequency analog signals will be distributed through the location's telephone network across unshielded twisted-pair wires, with the high-frequency signal sent to a gateway device for distribution to local devices such as personal computers, set-top boxes, and so on. The VDSL signal may be distributed across a 100 ohm VDSL twisted pair network within the customer premise, or in other cases may need to be distributed across a 75 ohm coaxial cable network. Either way, separation of signals must be accomplished without introducing unwanted interference into the digital signal.
Interference may be introduced into the VDSL signal from a number of sources. The low-frequency POTS signal may create transient interference signals during operation, for example, during on-hook, off-hook, and ringing. Other outside sources, including sources at a customer location or premise, or from a central office, may introduce electromagnetic interference or other types of interference into the VDSL signal.
Such interference must be prevented from being introduced into the VDSL signal, or removed from the signal, without significant data loss. This becomes especially true for video signals, a critical component of VDSL signals.
A number of splitter devices for interfacing customer premise equipment to the telephone network are already known in the industry. Many of these known splitter devices tend to incorporate extensive electronic schemes that include frequency splitters, multiple low-pass, high-pass, and bandpass filters, along with other active electronic devices. However, these known devices still often fail to satisfactorily eliminate transient signals introduced into the VDSL signals from the POTS circuit operation, especially in the higher frequency ranges. Furthermore, these devices tend to be sensitive to environmental changes, less robust, and sometimes more expensive than simpler analog devices.
On the other hand, industry has often slimmed analog splitters and filters as lacking the performance required for conditioning today's higher-and-higher frequency DSL signals. Analog filters with passive elements that are able achieve the steep roll-off characteristics necessary to separate voice and data signals require the use of higher-order filters. However, such higher-order filters tend to be complex, difficult to design, and relatively expensive due to the use of multiple inductors. Further, such designs tend to be very application specific, and do not always provide an interference free signal without significant data loss.
Therefore, a need exists for a simplistic, yet high performance, splitter device connected to a telephone company network that separates an incoming multi-frequency signal into separate low and high-frequency outputs with minimal distortion and data loss.